Reinforced concrete (RC) pile and prestressed high tensioned concrete spun (PHC) pile are capped at the ends with normal steel end plates that do not have a mechanical means to joint to each other except by site welding. It is cumbersome to use mechanical pile splices or connectors that consist of many small and fragile parts such as bolts, pins, washers, shear keys etc. In addition, these fragile parts of the connectors as mentioned above will require additional opened accesses such as grooves or holes that reduces the contact surface of the end plate for load transfer, and therefore the pile connectors must be fortified with flanges or wedges. Of recent, there are many patents filed in Korea that teach the use of various intermediate steel connectors that are used like adaptors placed in between the end plates of the spun piles. The use of an additional steel intermediate connector incurs extra cost. Further, these intermediate connectors are usually welded from smaller parts which tend to introduce additional weakness. Whereas in this invention, the end plate is hot forged from steel and precasted into ends of the spun pile
A pending patent PI2012700742 is filed in Malaysia by the same inventor that relates to an article for joining concrete piles which has overcame several drawbacks in the prior arts as referred to above. However in this present invention, many further improvements has been made as compared to PI2012700742; 1) The present end plate is designed to take heavy hammer impact without sustaining damages to the end plate's interlocking dovetail grooves. 2) In PI2012700742, thicker end plates are necessary to accommodate the prestressed steel tendon button head such that it is placed at least flush or below the top surface of the end plate and yet provide sufficient remaining depth in the end plate for the prestressed steel tendon seating to avoiding material punching failure through the base of the end plate. However in this invention, material savings is achieved by reducing the overall thickness of the steel end plate through creating segmental protrusions and segmental recesses of generally similar thickness, and in addition to this feature each segments have localised hot forged indentations that creates deeper sections for the prestressed steel tendon button head and seating. As a result of reducing the overall thickness, there is a material saving of at least 30% to 45% as compared to PI2012700742. 3) Another crucial feature lies in the 45 degrees rotation of the square openings to the vertical axis of the pile resulting in the edges of the segmental protrusion and recesses having like dovetail grooves when viewed from the side elevation. This 45 degrees orientation gives maximum contact surface between the tapered square pin and tapered square passageway. Further with this 45 degrees rotation, the tapered square opening can accommodate a tapered square pin that is 40% larger in size as compared to the prior art if the square pin is placed in the horizontal position. This is advantageous because by jamming and forcing the tapered square pins into the tapered square passageway of the mated end plates, it has higher axial compression force of 283% as that for the square pin placed in the horizontal position. The prior patent PI2012700742 specified a tapered passageway of a square shape but did not teach about the rotation angle in the axis of the pile. 4) The transfer of tension in the prestressed steel tendons across the connected piles is also improved by placing the vertical prestressed tendons in close proximity to horizontal interlocked tapered square pins instead of being located at the centre of the segmental protrusions or segmental recesses as in PI2012700742. Thus, when the pile is resisting a bending moment, the resulting additional tension in the vertical prestressed steel tendons will pull the end plate along the axis of the tendons and thereby bends the end plate, but this bending effect is considerably reduced by the close distance of the top and bottom vertical prestressed steel tendons to the horizontal interlocked tapered square pins. 5) To avoid seepage of grout through the end plate and the sides of the spun pile's mould during spinning, there is a provision to secure a circular steel skirt to the end plate by means of providing outer segmental side edges on the underside of the segmental protrusions so that there is sufficient thickness for a deep rectangular groove to traverse the circumference of the end plate such that it can embed the proximal lipped edge of the circular steel skirt. 6) In another adaptation of the present invention for use in a solid square concrete piles which is more common as compared to square hollow concrete piles, the alignment of the dovetail groove in the plan view of the end plate has been altered to avoid a sharp kink angle. A problem is encountered in the side milling process of a dovetail groove because a length of about half a diameter of the dovetail cutter to a sharp kink angle is obstructed. It is impossible to side mill the dovetail groove throughout its entire length unless there is a central opening in the end plate which is bigger than the diameter of the side mill cutter as in PI2012700742. Alternatively, this problem may be alleviated by using localised electrical induction to heat the interlocking edge of the end plate to about 1000° C. and hot forged the edge into a dovetail groove shape with specialised conforming die with the corresponding sharp kink angle, but this process is expensive as many specialised dies needs to be customised for different sizes of end plate.
In the CN 201120356388, this utility model claims a pre-stressing force concrete pipe pile machine fast connector is composed of tubular pile connected with the inclined plate in clamping block clamping block bolt and screw cap. Pipe pile is set in the connecting plate is symmetrically distributed with 3-8 radial locking groove each which is set on the bolt radial through hole at the inner ring of the groove with inner inclined clamping block the axial direction of the square hole. Outer clamping piece of inner surface of the gear shape of the outer surface of the clamping block is set in the centre of which is set on the bolt through hole. This utility teaches that the force derived from the clamping bolts is acting perpendicular to the vertical axis of the pile, and the horizontal clamping force is to grip the lateral edges of the pile into place by friction. Whereas in the present invention, the axial clamping force is derived not by tightening bolts but by jamming the tapered square pin which creates a expansionary force inside the tapered square passageway on the opposing contact surfaces along the grooves of the top segmental protrusion and the bottom segmental recess which finally presses the mated flat surfaces of the end plates very tightly together hence giving a stiffer performance under a pile bending moment.
An example of such pile connector is known in U.S. Pat. No. 4,157,230, whereby a nut is constructed within the joining ends of the two pile sections for a threaded bolt to be fastened to the nuts. The nut is provided with an annular groove having radially directed locking notches in the bottom. A locking disk is inserted into the groove. The disk has resilient locking tongues with radial edges which are directed against the unscrewing direction and which engage with the notches in the nut. One specific drawback is the dimensional accuracy required by this mechanical bolted splice as specified by the author is that the end surfaces of the abutting pile sections must be extremely plane in order to obtain as strong a connection between the sections as possible. Whereas in reality, under heavy hammer impact, the end surface be stressed and distorted.
In the EP0891454B1, the object of the invention is a stiff adjoining piece for joining concrete piles, particularly reinforced piles, end to end so that those ends of the concrete piles which are joined together comprise base plates that is provided with a cavity that receives the locking bar, and the groove extending as a toroid around the cavity, and with a hole extending from this groove at least approximately in a tangential direction; and of an insert pin which, when the pile joint is made, is driven into the hole so that it rums around the locking bar in the cavity, guided by the circumferential face of the groove, whereby it is simultaneously locked permanently in place because of plastically deformation. This invention specifically uses a round bar as a deformable lock pin whereas the present invention teaches the use of stiff tapered square pin.
In EP1403436A2, it concerns a pile connecting structure for connecting upper pile and lower pile to each other, at the connecting portion between the upper pile and the lower pile, by screwing bolts inserted in circular-shaped bolt inserting holes formed in the connecting to the bolt hole in the end plate of the pile on one side, where the head of the bolts screwed to the end plate of the pile on the other side is inserted in the large diameter portion of heteromorphic bolt insertion holes communicating between a large diameter portion which the head of the bolts formed on the connecting plate can pass through making the other pile and the connecting plate move relatively so that the bolts may shift from the large diameter portion of the heteromorphic bolt insertion holes to the small diameter portion. The drawback lies in that twice as many bolt insertion holes is required which weakens the pile connector and demands precision in manufacturing and also leads to difficulty in manipulating the bolts into the smaller diameter heteromorphic bolt insertion holes through twisting heavy piles. The current invention overcomes these problems during mating of the end plates with the tapered edges of the interlocking end plates and generous tolerance provided in the gaps to easily lower the segmental protrusions vertically into the segmental recesses. The tapered square pins can then be easily inserted and jammed into the tapered square passageway created by the mating of the end plates.